For the color-changing treatment of keratin fibers use is usually made of two coloring methods. In the first method, the coloration is produced with so-called oxidative or permanent colorants using a mixture of various developer substances and coupler substances and an oxidizing agent. If required, in this method, so-called direct (nonoxidative) dyes can be added to round off the coloring result or to produce particular color effects. The second method uses exclusively direct dyes, which are applied to the fibers in a suitable carrier mass. This method is easy to use, exceptionally gentle and is characterized by low damage to keratin fibers. The direct dyes used here are subject to a large number of requirements. For example, they have to be acceptable from a toxicological and dermatological point of view and allow the attainment of colorations in the desired intensity, which, inter alia, also requires adequate solubility in water. In addition, good lightfastness, acid fastness and rubbing fastness are required for the colorations achieved.
Compared with oxidative colorations, nonoxidative colorations, however, generally have lower durability and a poorer root to tip evenness of color. In addition, direct colorants are generally not able to “lighten” the hair since many direct dyes do not withstand the oxidizing agents required for the lightening and/or the required pH of greater than or equal to 9.
WO 95/01772 A1 discloses specific azo dyes and azomethine dyes as well as their use for dyeing keratinic fibers. WO 97/20545 A1 discloses enlightning dyeing compositions for keratinic fibers which contain specific cationic dyes with a —N═N— or —CH═N— group.
U.S. Pat. No. 3,573,287 discloses specific cationic azomethine compounds which are used for controlling infections of the urinary tract.